1. Field of The Invention
The present invention relates to a developing unit switching device for a printer on which attached are a plurality of developing units containing developers of different colors and, more specifically, to an improvement of the developing unit switching device.
2. Description of The Related Art
The applicant of the present invention has developed and filed a patent application of a multicolor printer connected to a host machine such as a word processor, a personal computer for business use and the like for printing various data such as characters, drawings, images as hard copies, which is capable of simultaneous multicolor printing on 1 page by selectively switching and driving a plurality of developing units containing developers of different colors.
Generally, an exposure position on the photoreceptor drum is different from a developing position where toner is applied on latent electrostatic images formed on the photoreceptor drum. Therefore, in a series of processes from exposure to development, there is inevitably a time lapse. Therefore, the switching between the plurality of developing units can be controlled by measuring the lapse of time by means of a timer or the like.
However, the above described control of the switching timing by means of the timer and the like has the following disadvantages. Namely, when the speed of processing such as exposure, development, and fixing is changed, for example the speed is increased, the time constant set in the timer for measuring the lapse of time must be changed. If the speed of rotation of the photoreceptor drum happens to be changed during the series of processes due to a mechanical or electrical cause, the predetermined position for switching the developer does not exactly coincide with the actual position of switching.